The present invention relates generally to a brake control system for use in motor vehicles, and more particularly to such a brake control system for suitably controlling the application of a braking force to each of wheels of a motor vehicle.
Brake systems in the vehicle braking art are so constructed that a hydraulic pressure generated through a booster in response to depression of a brake pedal is supplied through a hydraulic pressure passage device to wheel cylinders associated with wheels for the braking operation of the motor vehicle. Japanese Patent Provisional Publication No. 59-137245 discloses such a brake system including a braking control device for appropriately effecting the braking force distribution to the front and rear wheels of the motor vehicle, the braking control device comprising a proportioning valve to perform the pressure-decreasing control for the wheel cylinders associated with the rear wheels. Such a braking control device has disadvantages in that because of fixed boost ratio and braking force distribution, the braking effect does not correspond stably to the depressing force of the brake pedal due to variations of the vehicle loadage and frictional coefficient of the braking pad and the braking forces tend to be unbalanced between the front and rear wheels. In addition, during turning of the vehicle, the loads applied to the left and right wheels are varied, thereby causing an unbalance between the braking forces applied to the left and right wheels. These disadvantates would result in deterioration of the braking feeling.